Planographic printing



to obtain the aforesaid critical balance.

United States Patent Office Patented May 10, 1966 3,250,214 PLANOGRAPHIC PRINTING Kenneth Bricknell, East Finchley, London, England, as-

signor to A. B. Dick Company, Niles, Ill., a corporation of Illinois No Drawing. Filed Nov. 2, 1962, Ser. No. 235,107 Claims priority, application Great Britain, Nov. 6, 1961, 39,646/61 14 Claims. (Cl. 101-4492) This invention is concerned with improvements in or relating to planogralphic printing using paper base masters, i.e. masters having an exposed paper base surface. The master may consist wholly of such material or, alternatively, may comprise such material bonded to a substrate of e.g. plastic, metal or textile fabric, the master as a whole having sufficient flexibility for bending about a typewriter platen but with sufficient strength to maintain dimensional stability for at least the number of copies that is desired to produce therefrom.

In the art of planographic printing using paper base masters the normal procedure is first to render the surface of the master lithographic, then apply an oleophilic image to the paper master and finally apply a so-called etch composition to the imaged master so that the nonimaged areas become hydrophilio whilst leaving the imaged areas oleophilic. The treated master can then be used in an off-set planographic printing machine provided with ink and water fountains so that a reproduced image is transferred only from the imaged areas onto the oifset roller and thence onto the paper to be printed.

.The paper base master used in such a procedure frequently consists of a wet-strength paper coated with a series of coatings to obtain a lithographic surface, i.e., one having a critical balance of oleophilic and hydrophilic properties. Thus, if the surface is too oleophilic ink will not be attracted preferentially to the imaged areas but will in addition be picked up by non-imaged areas giving the phenomena of specking and scumming. If, on the other hand, the surface is too hydrophilic the ink will be repelled from the imaged areas and the greasy image will be unstable i.e. will tend to disappear from the surface of the master during use. Consequently considerable care is necessary in the selection of materials for and in preparation of the master in order For example, in one method of preparing paper masters, paper having a resin added to the pulp during the paper-making operation to confer so-called wet strength is first coated with a slurry of casein, clay and zinc oxide to provide an oil-receptive barrier coat, the barrier coat is coated with a slurry of clay and casein and this second coating is treated with a so-called wash coat comprising an aqueous solution of a polyvalent metal salt which confers lithographic properties on the clay-casein coat. The resultant master is brushed to a smooth finish and, provided due care has been exercised in the choice of materials and preparation of the master, will be found to possess to a greater or lesser degree the aforesaid critical balance. The master may then be imaged, treated with a so-called etch solution (frequently comprising a buffered solution of phosphoric acid) and utilized in a planegraphic printing process. Masters produced by this procedure are relatively expensive to produce and depend for their performance on having achieved the critical balance between oleophilic and hydrophilic properties.

It has now been found that it is possible to use paper masters prepared from paper having a critical balance of hydrophilic and oleophilic properties but which may, in fact, be distinctly oleophilic. Paper of this type is normally prepared by applying a slurry of ,a hydrophilic .copies planographically from imaged masters prepared from .paper of the art paper type, particularly if the paper has a high pick resistance, and the imaged master is subjected to a specific etch treatment prior to printing. The invention is, however, not limited to the use of such paper and may be used with paper having inferior oleophilic properties so long as it is oleophilic to some degree i.e. is able to pick up ink in' non-imaged areas when treated with a conventional phosphoric acid etch.

According to the invention, therefore, there is provided a method of preparing an imaged paper base master for use in a planographic printing process which comprises imaging the sur-face of a paper base, said surface being non-lithographic and oleophilic and which preferably has a high pick resistance, and subjecting the imaged surface to the action of an aqueous etch solution of an anionic macromolecular colloidal polyelectrolyte containing a high proportion of dissocia-ble anionic groups in order to desensitize the non-imaged areas. It is preferred that the polyelectrolyte contain one carboxyl group for each 50-1200 units of molecular weight.

By the term non-lithographic as applied to the paper surface is meant that an imaged surface of this nature is incapable of being drectly used in a planographic printing process when subjected to the action of an aqueous phosphoric acid etch solution.

By the term high pick resistance is meant a pick resistance of at least 7A and preferably at least 9A when determined on the dry surface of the master according to the standard Dennison Wax test.

The surface of the master should also preferably have high surface strength in the moist state. This may be achieved by the presenceof resins in the paper to confer wet strength.

Papers with a pick resistance of less than 7A and with \poor moist strength, are capable of producing a limited number of copies when used as masters in conjunction -with the etch solution according to the invention. However, from a practical viewpoint, papers of high pick resistance capable of printing from 25 to 300 or more copies are preferred.

The aqueous polyelectrolyte solution is preferably buffered to optimum pH conditions. Thus whilst wildly acid conditions enable one to achieve good image transfer from the commencement of the printing operations, if the solution is either too acid or. too alkaline it may be deleterious to the image on the master. It is, therefore, preferred though by no means essential, that the pH should be less than 7 and should also be at least 5 since it has been found that aqueous polyelectrolyte solutions having a pH within this range enable one to transfer a variety of images with good image transfer characteristics.

It is preferred that the polyelectrolyte used in the method according to the invention be a polymer of an acrylic acid of the general formula:

CH =CR-COOH where R represents a hydrogen or halogen (e.g. chlorine) atom or a lower alkyl group or a salt of said polymer, particularly polyacrylic acid itself or a salt e.g. an alkali metal or ammonium salt since these have given generally superior results.

The polymer of the above general formula may have a molecular weight of 1,000 to 100,000 as determined by solution viscosity methods, but in order to avoid undue viscosity of the etch solution, the molecular weight of the the solution drying out too rapidly. Humectants which may be used include, for example, glycerol, diethylene glycol, triethylene glycol, sonbitol and mannitol. V A further constituent which is desirably present in the solution but not, of course, in dissolved form, is an inert inorganic colloidal material e.g. colloidal silica, added in the form of a silica aquasol, in order to improve the running properties of the master and to reduce sensitivity towards handling. Other inert organic colloids which may be used include stannic acid, metasilicic acid, fluorosilicic acid and fiuoroboric acid, these acids existing in the colloidal state in the presence of the other ingredients in the etch solution to which they may conveniently be added as alkali metal or ammonium salts.

By inert as applied .to the inorganic colloid is meant that it is inert to the image and the paper surface.

Still'further ingredients which may be present include alkanols e.g. propanol and compatible wetting agents to facilitate wetting out of the master with the etch solution. The invention also includes within its scope a preferred form of the aqueous polyelectrolyte solution and accordingly the invention also provides aqueous solutions of an anionic macromolecular colloidal polyelectrolyte (e.g. a

polymer of an acrylic acid of the general formula CH =CR-COO H, as defined above, or of a salt of said polymer) having a pH of at least 5 but less than 7 containing a humectant and, if desired, an inert inorganic colloidal material e.g. colloidal silica. Preferably the solution contains ammonium and phosphate ions, e.g. it is an ammonium polyacrylate solution buffered with phosphoric acid.

Polyacrylic acids which may be used include polyacrylic acid itself, polymethacrylic acid and polychloroacrylic acid of which it is preferred to use polyacrylic acid itself.

The proportions of the various ingredients in the compositions according to the invention will of course vary according to factors such as the nature of the ingredients, viscosity of the composition, and the type of master used. For example, it may be necessary to vary the relative amount of the ingredients according to the oleophilicity of the master. However, the etch composition will, in

general, contain 02-10%, preferably 25%, by Weight of polyelectrolyte solids and 5-80%, preferably 30-50% by weight of humectant.

However, if the paper surface being treated has low oleophicility the amount of polyelectrolyte may be reduced, possibly below 0.2%. It will in general be convenient to prepare a single general purpose solution capable of treating papers having a variety of oleophilic properties. 7

If the solution contains an inert inorganic colloid this may be present in an amount of 0.003-0.3%, preferably 0.015-0. 12% by weight of inert colloid.

Where the polyelectrolyte is a polyacrylic acid this may be used in the form of an aqueous colloidal solution of the free acid or as an aqueous solution of a water-soluble salt e.g. the ammonium salt of the desired acid. The

solution is then adjusted to the desired pH value and a humectant and inert colloid added as desired.

After the imaged master has been subjected to the action of the etch solution according to the invention it is attached to the cylinder of an offset duplicator provided with ink and water fountains and copies taken in the usual manner.

An inherent advantage of the process according to the invention is that it can be used to reproduce images from imaged paper having the characteristics set forth above i.e. it can be used to make copies of pages in periodicals and books. A further advantage of the process according to the invention is that the paper surface prior to imaging is capable of receiving a stronger image, due to its inherent oleophilic characteristics, than paper surfaces which are lithographic.

In order that the invention may be well understood, the following examples are given by way of illustration only. In the examples and percentages are by weight.

Example 1 A composition was prepared having the following analysis:

Sedomax CP parts 20.40

An aqueous solution of anionic acrylic polymers sold by Imperial Chemical Industries Ltd. 'Ltz'l A silica aquasol (30% solids) sold by Monsanto Chemicals The composition (10 mls.) was then applied to an imaged master of commercial art paper having a pick resistance of 12A with an etch pad. The image had previously been produced on the master from a typewriter using a carbon and acotton ribbon and allowed to stand for 15 minutes. After treatment with the etch pad, the master was attached to the cylinder of a commercial offset duplicator provided with ink and water fountains and copies taken normally. In this way 150 satisfactory copies were obtained.

The examples was then repeated using a series of acrylic polymers of varying molecular weight, the polymer being used either in the form of the free acid or a salt. The compositions had the formulae given above except that the quantity of phosphoric acid used in the case of the acidic polymers was varied to produce a pH of 6.7-6.8 whilst in the case of the polyacrylate salts 0.88 ammonia was used in place of phosphoric acid but the pH was again adjusted to 6.7-6.8.

As polyacrylic acid or polyacrylate salt solutions were used the following:

(1) Polyacrylic acid approx. M.W. 90,000

(2) Ammonium polyacrylate approx. M.W. 70,000 (3) Polyacrylic acid, approx. M.W. 45,000

(4) Polyacrylic acid, approx. M.W. 10,000

(5) Sodium polyacrylate, approx. M.W. 2,000 (6) Ammonium polyacrylate, approx. M.W. 2,000 (7) Polyacrylic acid, approx. M.W. 1,800

All solutions (1)-(7) above contained approximately 15% w./w. solids, and were clear aqueous solutions of varying viscosity, depending on the degree of polymerisation of the polyacrylic acid.

Each etch was tested by applying it to an imaged master with a cotton etch pad, and running copies on a commercial offset duplicator provided with ink and water fountains. The masters were imaged from a typewriter using a carbon andsilk lithographic reproducing ribbon and were allowed to stand for about 15 minutes between imaging and running on the offset duplicator. Using as master paper commercial art papers of pick resistance values 11A and 12A respectively, the etches produced 50-75 and -120 good copies. On a master paper coated with hardened clay-casein of pick resistance greater than 14A the etches produced 300-500 good copies. Whilst all etches gave good results those in- Example 3 I composition was prepared havingthe following analysis:

-Acr'ytex W ..parts' 17.5 Glycerol do 37.6 Syton 2X do 0.21 Distilled water do 28.6 10% aqueous sodium hydroxide so1ut iondo 16.1 pH 11.3

An aqueous solution of polyacryllc acid of pH 3i0.5, containing 20% w/w of polymer of molecular weight about 20000-40000 and sold by Rohm and Haas G.m.b.H.

Used as in Example 1, this solution had a somewhat poorer densitising action on the background areas of the master and although affording good duplication of carbon paper and lithographic pen images, attacked images made with lithographic pencil and crayon to such an extent that they reproduced but faintly on the copies.

Example 4 A composition was prepared having the following analysis:

' AcrytexW parts 19.87 Glycerol do 42.57 85% phosphoric acid do 0.48 Syton 2X do 0.24 0.880 ammonia solution do 4.29 Distilled water do 32.54

Used as in Example 1, this solution produced 150 good copies with excellent reproduction of all types of image.

Example 5 A composition was prepared having the following analysis: Acrytex W parts 19.8 Glycerol do 42.45 Syton 2X do 0.20 0.880 ammonia solution do 3.14 Distilled water do 25.74 98% sulphuric acid do 1.78 pH 6.4

Used as in Example 1, this solution produced 100 good reproductions of all types of image.

Example 6 A composition was prepared having the following analysis:

Acrytex W parts 10.06 Glycerol -5 do 2.1.55 Syton 2X do 0.10 0.880 ammonia solution do 2. 17 Distilled water do 67.47 85% phosphoric acid do 0.24 pH 6.7

Used as in Example 1, this solution produced 82 copies with good reproduction of all images, but with poorer desensitisation of the background areas on which small specks of ink built up during the duplicating operation.

Example 7 Compositions were prepared having the following analysis parts by weight):

1 Ananlonlqlsurface active agent containing isopropanol manufactured by El'du' Pontd'e Nl'nours & 00.

Using as master paper commercial art-type papers of pickresistance 11A, 12A and 14A, respectively, imaged with type matter, each etch permitted the production of 50-75, 100-120, and 400-500 good copies respectively.

Example 8 Compositions were prepared having the following analysis:

. G. Sedomax CP 20.4 Glycerol 43.7 Distilled water 33.4 Inorganic compound 0.41

% phosphoric acid: sufiicient to give pH 6.7-6.8 in

each case.

The inorganic compounds used were respectively:

(i) Sodium stannate (ii) Soduirm metasilicate (iii) Ammonium fluorosilicate (iv) Sodium fluoborate Used as in Example 1 in conjunction with art paper of pick resistance 12A, (i), (iii) and (iv), gave 75-100 good copies, (ii) gave 50-75 good copies.

It should be noted that the compounds (i)-(iv) above in the mildly acidic compositions are converted to stannic, metasilicic, fluorosilic and fluoboric acids respectively, and in the presence of the other ingredients of the compositions the four acids exist in a colloidal state.

I claim:

1. A method of preparing an imaged paper base master for use in a planographic printing process which comprises imaging the surface of a paper base, said surface being non-lithographic and oleophilic, and subjecting the imaged surface to the action of an aqueous solution containing a polyelectrolyte selected from the group consisting of polymers of acrylic acids of the general formula:

CH =CR COOH where R is a member selected from the consisting of hydrogen and halogen atoms and lower alkyl groups, and soluble salts of said polymers.

2. A method as defined in claim 1 in which the polyelectrolyte has a molecular weight of 1,500 to 10,000.

3. A method as defined in claim 1 in which the aqueous etch solution contains 02-10% by weight of polyelectrolyte.

4. A method as defined in claim 1 in which the etch solution has a pH of at least 5 and less than 7.

5. A method as defined in claim 1 in which the etch solution contains a humectant.

6. A method as defined in claim 5 in which the etch solution contains 580% by weight of humectant.

7. A method as defined in claim 1 in which the etch solution contains an inert inorganic colloid.

8. A method as defined in claim 7 in which the etch solution contains 0.00'3-0.3% by weight of inert inorganic colloid.

9. A composition for use in the conversion of the oleophilic non-imaged surface portions of an imaged planographic printing plate to convert the oleophilic nonim aged portions to a hydrophilic water receptive surface comprising a solution having a pH of at least 5 and less than 7 comprising water, a humectant and an anionic macromolecular colloidal polyelectrolyte, said polyelectrolyte containing a high proportion of dissoluble anionic groups and in which the polyelectrolyte contains one carboxyl group for each 50-1200 units of molecular weight, and in which the polyelectrolyte is selected from the group consisting of polymers of acrylic acids of the general formula:

CH =CR-COOH where R is a member selected from the group consisting of hydrogen and halogen atoms and lower alkyl groups, and salts of said polymers.

10. A solution as defined in claim 9 which contains ammonium and phosphate ions.

11. A solution as defined in claim 9 in which the polyelectrolyte has a molecular weight of 1,000 to 100,000.

12. A solution as defined in claim 9 which contains 02-10% by weight of polyelectrolyte solids and 580% by weight of humectant.

13. A solution as defined in claim 9 which contains an inert inorganic colloid.

14. A solution as defined in claim 13 which contains 0.003-0.3% by weight of inert inorganic colloid.

References Cited by the Examiner UNITED STATES PATENTS 2,534,650 -12/1950 Worthen 10l149.2 2,582,347 1/1952 Newman 10ll49.2 2,589,313 3/1952 Wood l0l,l49.2 3,028,804 4/1962 Neuegebauer et al. 10l--l49.2 3,107,169 10/1963 Bornarth 101---149.2 -X

DAVID KLEIN, Primary Examiner.

. WILLIAM B. PENN, Examiner. 

9. A COMPOSITION FOR USE IN THE CONVERSION OF THE OLEOPHILIC NON-IMAGED SURFACE PORTIONS OF AN IMAGED PLANOGRAPHIC PRINTING PLATE TO CONVERT THE OLEOPHILIC NONIMAGED PORTIONS TO A HYDROPHILIC WATER RECEPTIVE SURFACE COMPRISING A SOLUTION HAVING A PH OF AT LEAST 5 AND LESS THAN 7 COMPRISING WATER, A HUMECTANT AND AN ANIONIC MACROMOLECULAR COLLOIDAL POLYELECTROLYTE, SAID POLYELECTROLYTE CONTAINING A HIGH PORTION OF DISSOLUBLE ANIONIC GROUPS AND IN WHICH THE POLYELECTROLYTE CONTAINS ONE CARBOXYL GROUP FOR EACH 50-1200 UNITS OF MOLECULAR WEIGHT, AND IN WHICH THE POLYELECTROLYTE IS SELECTED FROM THE GROUP CONSISTING OF POLYMERS OF ACRYLIC ACIDS OF THE GENERAL FORMULA: 